GB933742A - Slow burning delay device - Google Patents

Abstract

933,742. Detonators and delay compositions therefor. CANADIAN INDUSTRIES Ltd. Nov. 24, 1961 [Dec. 9, 1960], No. 42102/61. Class 9 (1). A delay device for a detonator comprises a slow-burning composition of an intimate mixture of 60-85 parts by weight of finely divided iron and 40- 15 parts by weight of powdered sulphur interposed between an explosive charge and an ignition means. In the embodiment described an electric delay detonator comprises a charge 4 of the delay composition, a primer 3 of lead azide or a mixture of lead azide and lead styphnate and an explosive charge 2 which may be of pentaerythritol tetranitrate. An air gap 10 separates the delay composition from a plastics cup 7 containing an ignition composition 6 and a bridge wire 5. In a modification of this embodiment the air gap 10 and cup 7 are dispensed with and an ignition composition comprising 98 parts by weight of red lead and 2 parts by parts by weight of boron is directly embedded in the delay composition. According to the invention, speed of burning of the composition largely depends on the proportions by weight and the particle sizes of the constituents, the latter being conveniently expressed in terms of specific surface (cm<SP>2</SP>/g). In a preferred form the composition comprises 65-75 parts by weight of iron and 35-25 parts by weight of sulphur, the iron having a specific surface of less than 1000 cm<SP>2</SP>/g. The burning rate may be reduced by the addition of an inert diluent such as finely divided silica, talc or titania. Tables of results showing variation of burning speed with proportions, particle size. and bulk density of constituents are given.